Boring bar sleeves; what type and where to find?

D

dml66

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I've read this post many times and want to up my boring game since I'm using the worst boring bar holder; the lowly OXA-2.

https://www.hobby-machinist.com/threads/a-boring-primer.75721/

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The post shows another QCTP holder, the OXA-4, which natively holds boring bars with 1/2" and 3/8" round shanks but, with the addition of a boring bar sleeve, may be used with smaller boring bars.

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The sleeve shown appears to be a compression type, slit longitudinally, I've not found these anywhere.

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I've found other sleeves, like the one below from Micro 100, it appears to use a setscrew to secure the boring bar at the head end.

1780096007031.png

In any event, while I don't have, nor plan to have a 100+ boring bars, I'd prefer to have a set of sleeves that cover the full range of boring bar diameters without taking out a loan.

Any ideas on this?
 
Well I'm far from a boring bar expert, but so far my thought has been with small bars something like your OXA-2 is fine for small bars.
But you gain some rigidity going to the OXA-4 style when your bar diameters increase.
Basically I'm not so sure you would gain anything by getting sleeves for less than 3/8"
I'm more than willing to be told I'm mistaken though.
 
Justin.P said:
Well I'm far from a boring bar expert, but so far my thought has been with small bars something like your OXA-2 is fine for small bars.
But you gain some rigidity going to the OXA-4 style when your bar diameters increase.
Basically I'm not so sure you would gain anything by getting sleeves for less than 3/8"
I'm more than willing to be told I'm mistaken though.
Click to expand...
I'm inclined to agree. What I've experienced is boring bars for, lets say a 7/16" diameter hole, when set to 1" or so stick out, will deflect noticeably, even in AL. When I power feed the bar in and out, remove the chip load, gage the hole, then run the bar back in and out again, there's still a notable chip load, and the bore grows. I've learned not to trust a one-and-done unless it's a <0.0001" DOC. I'm trying hard to convince myself this is due to the holder and not the bar itself.
 
Easy enough to make your own sleeves, I make my own OD/ID steel sleeves and run a slit along the length. I have modified the boring bar holder with a set screw that is on center with the boring bar and goes through the sleeve to align the different diameter boring bars to the same horizontal position. Smaller boring bars say under 3/8" would benefit from a sleeve (and sometime a bit longer then the holder) vs a #2 holder which has a bottom V grove and locking screws.

The type of boring bar material as well as insert type and DOC play a large role in the ability to maintain consistent diameter end to end, as well as chatter. I have done through bore milling with 4140 and able to maintain a 7" long through hole to better than 0.001" with a 1" carbide boring bar. Typically the inserts are either positive rake or neutral with a high positive rake edge for better cutting performance. My previous experience with steel boring bars was pretty dismal. Carbide is much stiffer and can bore deeper, but also more prone to snapping inparticular the smaller bars.

Slitting the sleeve.
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Added set screw that goes through the sleeve to press on the top flat of the boring bar. FYI, most holders are case hardened so most drills will not punch through the outer layer. I used a center drill to start the hole and usually will burn up a HSS drill in the process of drilling through the holder. Use a spiral tip tap with plenty of oil to tap the hole. Below is boring 1144, depth is 4" with quite a bit of stickout of the carbide boring bar. The boring bar holder has sleeves for 5/8", 3/4" and 1" boring bars that fit into the holder.
1780118843679.jpeg
 
These are the ones I have. I have 2 of each size but I also have a CXA tool post system. So sometime I use 2 when the bar extends enough in to the holder. Sometime only one.

Generally most machinists will use a bushing or sleeve with a bar in any machine as it helps break up harmonics in the cutting process, I have found this to be true. The split bushings or sleeves do a better job.


They sure have become proud of these in the last 25 years, I think I paid about $10 a piece back in the early 2000's. Good thing is they do last forever. Looking at the prices today, I would likely just make one if I need one.
 
dml66 said:
I'm inclined to agree. What I've experienced is boring bars for, lets say a 7/16" diameter hole, when set to 1" or so stick out, will deflect noticeably, even in AL. When I power feed the bar in and out, remove the chip load, gage the hole, then run the bar back in and out again, there's still a notable chip load, and the bore grows. I've learned not to trust a one-and-done unless it's a <0.0001" DOC. I'm trying hard to convince myself this is due to the holder and not the bar itself.
Click to expand...
Carbide boring bars have significantly less deflection.
 
Shade Tree Welder said:
true and a much higher price tag.

deflection is predictable, as long as your depth of cut is consistent.
Click to expand...
That makes sense. I recently completed a tapered hole project, the starting hole was drilled; a straight hole. Until the full length of the hole became tapered by the boring bar, the exhumed chip load was bizarre, no doubt because the DOC varies from one end to the other. Once tapered, the chip loads and ID growth became more predictable than not. In other words, boring bar deflection appears to be a constant force per pass regardless of where the cutter is in the hole, as long as the boring bar is fully responsible for the starting hole.
 
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